Widely heralded as the “antidote” to opioid overdoses, naloxone was first patented in New York in 1961 by scientists looking to treat constipation caused by chronic opioid use. Despite being related to morphine, naloxone has almost no painkilling properties, but researchers quickly recognized its ability to block opioid receptors in the central nervous system. Injections take effect in about two minutes and nasal sprays in about five minutes, restoring breathing and returning the victim to consciousness. Naloxone itself has almost no side effects. Opioid users wake to withdrawal symptoms, which can be very unpleasant but not generally dangerous.

In 1971 the Food and Drug Administration approved naloxone for treating opioid overdoses by intravenous or intramuscular injection. As opioid use increased in the 1990s, medical professionals began experimenting with new techniques to administer naloxone quickly and safely under non-hospital conditions.

In 1996, 15 states and Washington, D.C., began piloting take-home naloxone kits for laypersons. The results of these programs have been enormously positive. From 1996 through 2014, more than 26,000 opioid overdoses were reversed by non-medical personnel, the CDC reports.

Naloxone also has other uses. Some manufacturers include naloxone in their abuse-deterrent formulations of opioid tablets because it is not effective if taken orally. But if the tablet is crushed for injecting or snorting, the naloxone blocks any potential high. Naloxone also has been used to treat types of shock because it seems to increase blood flow.

The CDC now encourages naloxone kits be provided to any laypersons close to opioid users, patients in substance use treatment programs, convicts upon their release from prison, and patients who receive chronic opioid prescriptions. Because naloxone is metabolized faster than most opioids, repeated doses may be necessary if an overdose begins to recur.